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Reflected hidden faces in photographs revealed
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The pupil of the eye in a photograph of a face can be mined for hidden information, such as reflected faces of the photographer and bystanders, according to research led by Dr. Rob Jenkins, of the Department of Psychology at the University of York and published in PLOS ONE (open access).
The researchers say that in crimes in which the victims are photographed, such as hostage taking or child sex abuse, reflections in the eyes of the photographic subject could help to identify perpetrators. Images of people retrieved from cameras seized as evidence during criminal investigations could be used to piece together networks of associates or to link individuals to particular locations.
By zooming in on high-resolution passport-style photographs, Jenkins and co-researcher Christie Kerr of the School of Psychology, University of Glasgow were able to recover bystander images that could be identified accurately by observers, despite their low resolution.
To establish whether these bystanders could be identified from the reflection images, the researchers presented them as stimuli in a face-matching task. Observers who were unfamiliar with the bystanders' faces performed at 71 per cent accuracy, while participants who were familiar with the faces performed at 84 per cent accuracy. In a test of spontaneous recognition, observers could reliably name a familiar face from an eye reflection image.
"The pupil of the eye is like a black mirror," said Jenkins. "To enhance the image, you have to zoom in and adjust the contrast. A face image that is recovered from a reflection in the subject's eye is about 30,000 times smaller than the subject's face." In the research, the whole-face area for the reflected bystanders was 322 pixels on average.
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